This invention relates to a semiconductor device of the so-called wafer level CSP type and its manufacturing method in which the packaging of a semiconductor chip is realized in the wafer state.
In the semiconductor device manufacturing industry, efforts are continuing for the purpose of further downsizing a single package semiconductor device. The initial effort for the purpose of realizing miniaturization of a semiconductor device reduced the size of the semiconductor chip itself. By making the semiconductor chip smaller, the number of chips that could be obtained from one wafer was increased, and along with bringing down manufacturing costs, since the movement distance of electrons between each element could be made shorter, the operating speed was increased. Due to the development of microscopic processing technology, decreasing the chip size for a semiconductor device having the same functions became possible. The current leading-edge design guideline is less than 0.18 xcexcm, and by this means, it has become possible to place more than two million units on a single semiconductor chip.
In order to realize a miniaturization of the semiconductor device, the next effort involved making the size of the package in which a chip is sealed as close as possible to the size of the semiconductor chip it houses. As one result related to this effort, a type of semiconductor device was created called a chip size package (Chip Size Package:CSP) or a chip scale package (Chip Scale Package). The connecting terminals (for example, solder balls, hereinafter, called external connecting terminals) for the printed circuit board on which the semiconductor device is mounted form a two-dimensional arrangement on the face of a semiconductor chip, and was successful in bringing the size of the package close to the chip size. By decreasing the above-mentioned package size so as to approach the semiconductor chip size, along with the mounting surface area becoming small, the wiring length that connected the terminals on the chip and the external connecting terminals became short, and by this means, in the same manner as when decreasing the size of above-mentioned semiconductor chip itself, the operating speed of the semiconductor device was increased.
However, even when the package size was decreased, the manufacturing cost could not be lowered very much. Because various processes for the packaging were conducted for each individual semiconductor chip cut out from the wafer, even if the package size was decreased, because the number of processes was fixed, there were no changes in productivity.
With this background, technology that packages a semiconductor chip as is in the wafer state (hereinafter, called wafer level CSP) has been proposed, and development is continuing in the direction of its realization by individual companies. Semiconductor manufacturing technology that executes packaging at a stage before individual semiconductor chips are cut away from the wafer is referred to as wafer level CSP. In wafer level CSP, since the packaging process can be done as one unit with the wafer process, the packaging cost, and by extension, the manufacturing cost of the semiconductor, can advantageously be greatly lowered. In regard to the further detailed content of wafer level CSP, please refer to the xe2x80x9cNikkei BP Company publication, Nikkei Micro-device, 1998 August Issue, Pages 44 to 71.xe2x80x9d
On the one hand, in a wafer level CSP, in the same manner as in a conventional CSP type semiconductor device, there are problems in mounting reliability in relation to the printed circuit board. In thermal cycle tests of this type of semiconductor device, cracks are generated in the junction portion of the external connecting terminals of the printed circuit board, and there are instances when the junction is open and defective. The main cause is stress based on linear expansion coefficient differences between the semiconductor chip made of silicon and the printed circuit board made of FR4 or the like, and a means that relieves this must be devised in the design for a wafer level CSP.
Thus, as a method that absorbs the linear expansion coefficient difference between the above-mentioned semiconductor chip and the printed circuit board, and by this means relieves the stress, a construction has been proposed wherein a metallic supporting post is formed on the wiring pattern of the semiconductor chip main face, and an external connecting terminal comprising a solder ball or the like is bonded on top of the said supporting post. In said semiconductor device, the main face of the above-mentioned semiconductor chip and the surrounding of the supporting post are covered by resin. Due to the fact that the above-mentioned supporting post is interposed between the external connecting terminal that is directly bonded to the printed circuit board and the semiconductor chip, the generation of the above-mentioned stress can be relieved by means of deformation of said supporting post element.
However, a semiconductor device that is equipped with the above-mentioned metallic supporting posts has the following types of problems.
(1) Time and expense are required in forming the metallic supporting posts on the main face of the semiconductor chip. In other words, the abovementioned metallic supporting posts are formed by means of accumulating a metal plating (for example, copper plating) on the wiring pattern. In order to relieve the above-mentioned stress, it is necessary for said supporting posts to have a height of more than 100 xcexcm, and more than two hours are required to form these supporting posts by means of the plating method. In order to further improve the mounting reliability for the semiconductor device, it is necessary to further heighten the supporting posts, (for example, to more than 200 xcexcm), and realization of that is extremely difficult from the aspects of time and cost.
(2) In the case of forming the metallic supporting posts by means of a plating method, because their shape and material cannot be freely selected, the degree of freedom for the design of the target package is limited.
Therefore, the objective of this invention, in a semiconductor device referred to as a wafer level CSP, is to improve its productivity while ensuring its mounting reliability.
In order to achieve the above-mentioned objective, the semiconductor device of this invention has a semiconductor chip having electrode pads that are electrically connected to electrical circuits that are formed on the main surface of a semiconductor substrate, conductive supporting posts of nearly spherical shape that are provided on the above-mentioned semiconductor chip and which are electrically connected to the above-mentioned electrode pads, resin that is formed so that the sections of the above-mentioned electrode supporting posts are exposed on the above-mentioned semiconductor chip, and external connecting terminals that are provided on the tips of the above-mentioned conductive supporting posts.
In a preferred embodiment configuration, the above-mentioned electrode pads and the above-mentioned conductive supporting posts are electrically connected by means of wiring that is formed on above-mentioned semiconductor chip. Also, it is preferable that the above-mentioned external connecting terminals be solder balls, and more preferably, that the above-mentioned conductive supporting posts be constructed by means of nearly spherical copper balls and solder that covers the surface of said copper balls. Furthermore, it is preferable that the height of the above-mentioned conductive supporting posts be more than 200 xcexcm.
Also, the manufacturing method for a semiconductor device of this invention has a process that prepares a wafer on which semiconductor elements are formed having electrical circuits and electrode pads that are electrically connected to said electrical circuits, a process that forms wiring for the purpose of connecting external connecting terminals and the above-mentioned electrode pads on the above-mentioned semiconductor elements, a process that connects preformed conductive supporting posts to prescribed positions of the above-mentioned wiring, a process that forms resin so that the tips of the above-mentioned conductive supporting posts on the above-mentioned semiconductor element are exposed, a process that forms external connecting terminals on the tips of the above-mentioned conductive supporting posts, and a process that produces semiconductor devices on which external connecting terminals are formed by dicing the above-mentioned wafer.
Also, it is preferable that the process that forms the above-mentioned resin contains a process that supplies a flexible resin on top of the above-mentioned semiconductor chip and cures it, and a process that exposes the tips of the above-mentioned conductive supporting posts by grinding the upper section of the surface of the above-mentioned resin and the upper portion of the above-mentioned conductive supporting posts.
In this invention, since the forming of the supporting posts for the purpose of the external connecting terminals can be done by carrying and connecting conductive supporting posts to the desired positions of the wiring, supporting posts of the target height can be obtained in an extremely short time compared to that required for forming of supporting posts by means of the plating method used in the past. By this means, a degree of freedom in the design of the supporting posts can be obtained, and in that way, supporting posts of sufficient dimensions, shape, and materials necessary for obtaining mounting reliability for the package can be obtained.
Also, it is preferable that the above-mentioned conductive supporting posts be constructed by means of nearly spherical copper balls and solder that covers the surface of said copper balls, and it is preferable that the process that connects the above-mentioned conductive supporting posts contain a process that carries the above-mentioned conductive supporting posts to prescribed positions on the above-mentioned wiring, and a process that connects said conductive supporting posts to prescribed positions of the above-mentioned wiring by melting the surface solder of the above-mentioned conductive supporting posts. Furthermore, it is preferable that the process that forms the above-mentioned external connecting terminals contain a process that carries solder balls to the tips of the above-mentioned conductive supporting posts, and a process that connects said solder balls to the above-mentioned conductive supporting posts by melting the above-mentioned solder balls.